I do want to build a very simple Single Page Application. There will be a backend (NodeJS-App) and a Frontend (AngularJS).
What is the best approach to deploy this in an Azure Web App? Can I host both in the same App or should I create two separate apps? One hosting the backend and another one just serving the static files of the Angular app?
Are there other (maybe better) solutions?
I'll throw out two separate answers.
If you go the WebApp route, you do not need two separate WebApps. You can execute your NodeJS code and serve static Angular templates and controllers from the same WebApp.
Instead of going the WebApp route, consider using an Azure Function to host your NodeJS app. You can then serve static Angular files from Azure Blob Storage. The advantage of this approach are possibly cost and ease of scalability. This article walks you through doing so.